The areal metal elements described in this prepublished German patent application are used, for example, for the manufacture of sectional elements, in particular of upright sections or plaster sections. The metal elements in this connection have incisions in their mid regions which are shaped such that, when the metal elements are drawn apart, metal regions present between the incisions are folded over so that ultimately a widening of the metal element takes place. Wider metal elements can thus be produced with a reduced metal consumption by this folding procedure. The cutting patterns required for the folding procedure can be of the most varied type. A plurality of such different cutting patterns are described in German patent application 102 59 307.8 and are in particular shown in FIGS. 1-22 of this application. For the better understanding of the present application, the disclosure content of German patent application 102 59 307.8, in particular with respect to the specifically described and shown cutting patterns, are explicitly included and incorporated by reference in the content of the present application. The metal elements in the sense of the present invention are made areal or flat at least in the region of the cutting patterns. In other regions, for example also in the region of the longitudinal sides of the metal elements, the metal elements can also deviate from the areal or flat shape. Thickened regions, steps or bent over regions can in particular be formed at the longitudinal sides. The metal elements can thus e.g. already be preshaped as U-shaped sections or C-shaped sections.
It is, however, problematic to carry out the expansion of such elongated metal elements which are areal at least regionally with an economically justifiable effort and so to achieve an economically sensible manufacture of the sectional elements. Since the costs of such sectional elements are mainly determined by the material costs, a widening of the metal element is admittedly generally desired with a reduced material requirement, but the gains recorded by the material saving many not be cancelled out again by increased costs in the production of the sectional elements. An economically worthwhile manufacture is the more difficult in this connection since corresponding sectional elements represent a mass produced article of which thousands of kilometers are produced annually and which is produced at a very high speed (for example 100 to 150 m/min). An apparatus for the expansion of corresponding areal or flat metal elements must therefore be capable of ensuring a correspondingly high throughput with a simultaneous high reliability.